The conformal limit of inflation in the era of CMB polarimetry

Enrico Pajer, Guilherme L. Pimentel, Jaap V.S.V. Van Wijck

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

We argue that the non-detection of primordial tensor modes has taught us a great deal about the primordial universe. In single-field slow-roll inflation, the current upper bound on the tensor-to-scalar ratio, r<0.07 (95% CL), implies that the Hubble slow-roll parameters obey η , and therefore establishes the existence of a new hierarchy. We dub this regime the conformal limit of (slow-roll) inflation, and show that it includes Starobinsky-like inflation as well as all viable single-field models with a sub-Planckian field excursion. In this limit, all primordial correlators are constrained by the full conformal group to leading non-trivial order in slow-roll. This fixes the power spectrum and the full bispectrum, and leads to the ''conformal'' shape of non-Gaussianity. The size of non-Gaussianity is related to the running of the spectral index by a consistency condition, and therefore it is expected to be small. In passing, we clarify the role of boundary terms in the ζ action, the order to which constraint equations need to be solved, and re-derive our results using the Wheeler-deWitt formalism.

Original languageEnglish
Article number009
JournalJournal of Cosmology and Astroparticle Physics
Volume2017
Issue number6
DOIs
Publication statusPublished - 7 Jun 2017

Keywords

  • Inflation
  • non-gaussianity
  • quantum cosmology

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